/Engine/Source/Runtime/Core/Public/GenericPlatform/GenericPlatformFile.h
Returns the number of bytes that are currently allowed to be written to throttled write storage (if the platform has such restrictions)
The number of bytes that are allowed to be written to write throttled storage. If there is no limit, INT64_MAX is returned
virtual int64 GetAllowedBytesToWriteThrottledStorage ( const TCHAR * DestinationPath )